1. Field of the Invention
The present invention generally relates to an operation of a lamp. The present invention specifically relates to filament cutback.
2. Description of the Related Art
When lamps are operated by a programmed-start ballast, which by definition requires heating,of the lamp filaments before lamp ignition, the lamp life is increased. The heating of the lamp filaments typically cease upon lamp ignition in order to reduce losses during normal operation of the lamp. Also, it is important not to exceed the lead current limits given by the lamp manufacturer. Hence, a good filament cutback circuit is necessary for improved lamp performance and reduced power loss at normal operation.
One filament cutback circuit as known in the art employs a capacitor in series with a filament winding and a filament to achieve a first-order cut back. A second filament cutback circuit as known in the art employs a parallel coupling of a capacitor and an inductor coupled in series between the filament winding and the filament. This circuit operates as a low impedance circuit during a preheating of the lamp filaments, and as an open circuit (i.e., infinite impedance) during normal operation of the lamp. A third filament cutback circuit as known in the art employs a series coupling of a capacitor and an inductor coupled in series between the filament winding and the filament. This circuit operates as a short circuit (i.e., zero impedance) during a preheating of the lamp filaments, and as a high impedance circuit during normal operation of the lamp.
The present invention is an improvement over the aforementioned prior art filament cut-back circuits.
The present invention is a filament cut-back circuit. Various aspects of the present invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
One form of the present inventions is a filament cut-back circuit comprising a filament winding and an impedance circuit in electrical communication with said filament winding. The impedance circuit operates as a short circuit in response to a reception of an alternating voltage at a preheat frequency. The impedance circuit operates as an open circuit in response to a reception of an alternating voltage at an operating frequency.